Pneumatic gage



Nov. 26, 1957v c. A. WHITNEY ETAL 2,814,121

PNEUMATI'C GAGE Filed Jan. 4. 195e 2 sheets-sheet 1 INVENTORS CHARLES A-WHITNEY WAYNE E-. TINKER v M//TTO ,J

Nov. 26, 1957 c. A. WHITNEY x-:T A1. 2,814,121

PNEUMATIC GAGE Filed Jan. 4, 1956 2 Sheets-Sheet 2 I ,f/ l a' a ATTORNEYUnited States Paten-t PNEUMATIC GAGE Charles A. Whitney, Bloomfield, andWayne E. Tinker, Granby, Conn., assignors to Pratt & Whitney Company,Incorporated, West Hartford, Conn., a corporation of DelawareApplication January 4, 1956, Serial No. 557,311

Claims. (Cl. 33f147) is essentially non-linear, and only a relativelysmall portion of the resulting pressure vs. clearance curve issufficiently linear to permit its adaption for gaging purposes.

The pneumatic circuit of an air operated dimensional gage is relativelysimple. In o ne type of circuit, air from a source of supply is passedthrough a pressure regulator and a restriction valve arranged intandem.v From this valve, the air is conveyed to the inlet end of theair cartridge, a pressure indicating gage being serially connectedbetween the inlet of the cartridge and the restriction valve. Thecartridge is. provided with a longitudinal bore and a plurality ofpassages providing pneumatic communication between the bore interior andthe atmosphere. A piston member is arranged for sliding axialdisplacement within the bore, and adapted to variably uncover or closethese passages, the amount of air permitted to escapefrom the cartridgethrough the passages being a function ,ofthe axial displacement `of thepiston memben The airpressureto the cartridge inlet` forces the outerend Aof the piston`4 member into Vcontact with the piece being gaged.

The resulting pressure drop appearing inthe pressure indicatingV gageprovides the dimensional intelligence which is sought.`

t As previously mentioned,'since` the relationship between pressure dropand clearance is linear only over a small portion of its, plotted curve,it becomes a problem for the operator vto first calibratel the pneumaticcomparator and cartridge before putting the gage to use.

The prior artrhas not solved `this problem` of calibrationsatisfactorily and in currentV practice it is entirely fortuitous thatan operator will locatethe linear portion f of operation after areasonable number of tries. The problem of adjustment is complicated byVthe fact that essentially three factors are involved; the pressure ofthe air in the' intake of the cartridge as shown on thel indicatingmeter, theV amount ofopening in the restriction valve, and the initialclearance point (the point selected for zero on the indicating-` meteras determined by a predetermined displacement of the piston member).Thesethree factors are interrelated, and"selectionof any two of themdetermines' rthe third. For any given magnitude of` pressure supply,there is onlyl onecurve which will satisfy the re'- quirementsforlineargaging. Further, for each selected crnbination of factors there arewholefamilies of curves, so that the number. of possible choices is extremelywide. v Moreover, it should be borne inmind that the operator does nothave these families of curves before him so that his choice of factorsto be manipulated must be based on an intelligent appraisal of what istaking place as he manipulates these various factors. i t A j v111itspreferred form theaircartridge for; useiwith a pneumatic comparatorgage in accordance with the present invention comprises a barrel memberhaving a longitudinal bore therein and a plurality of passages provtdlngpneumatic communication between the bore and the at mosphere. The barrelincludes an intake end serially connected to a source of air underpressure and to a gaging meter on the comparator. Piston means aremounted for axial displacement within the bore, and are adapted tovariably uncover or close these passages as a function of its axialdisplacement. Calibrated means mounted on the barrel enable precisedetermination of specic displacements of the piston means, so that thepneumatic comparator gage may be quickly calibrated to provide a linearrelationship between the pressure in the barrel intake and thedisplacement of the piston means over a pre# selected range of movementthereof.

Accordingly, it is an object of this invention to provide an improvedair cartridge which enables the operator to quickly calibrate theassociated pneumatic comparator gaging circuit.

A further object is to provide a novel air cartridge havingA reliablecalibration means of simple and inexpensive construction.

The novel features which are believed to be characterf istic of thisinvention are set forth with particularity in the appended claims. Theinvention itself, however, both as to its organization and method ofoperation, together with further objects and advantages thereof, maybest be understood by reference to the following description taken inconnection with the accompanying drawings in which:

Figure l is a pictorial showing of the general role played by the aircartridge in pneumatic gaging;

Fig. 2 is a schematic of the pneumatic circuit including the aircartridge in accordance with one illustrative embodiment of the presentinvention;

Fig. 3A is a diagram showing the pressure-nozzle clearance curve for atypical air gage;

Fig. 3B is a diagram showing the pressure-nozzle clearance family ofcurves of a typical air gage with only the opening of the airrestriction valve being Varied;

Fig. 3C is a diagram showing a similar family of curves when the supplypressure is varied, all `other factors being held constant;

Fig. 4 is a sectional view of the air cartridge unit in accordance withone illustrative embodiment of the invention;

Fig. 5 is a view taken along the line 5-5 of Fig. 4;

Fig. 6 is a sectional view showing the barrel member proper; and

Figs. 7 and 8 are pictorial views showing how the calibration means areadjusted in accordance with the present invention.

Before proceeding with a detailed description of the air cartridge unitaccording to this invention, it will be helpful to consider thefollowing brief account of the role played by the air cartridge in theoverall problem of pneumatic comparator gaging.

Referring now to Fig. l, let us assume that Aa work piece 10 is to bechecked for accuracy in its height dimension. The operator first checksthe magnification ofthe air cartridge comparator combination by anyconvenient standards, such as Holte blocks 12 for example. These blocksare placed on a stand or base 14, and assembled in numbers sufficient toequal the desired dimension as well as the maximum and minimumdeviations therefrom respectively. The base 14 may be a granite slab ,ora piece of steel carefully treated or lapped to provide a perfectlyplanar support. The cartridge unit indicated generally at 16 is coupledto a hose line 18 by means `of a fitting 20 screwed to the threaded end(Fig. 4: 64) -thereof.` The cartridge unit is held in xed position bymeans of a suitable clamping means 22.

Air under pressure is fed via conduit 24 to an Air- O-Limit comparatorindicated generally at 26. The pneumatic comparator internally houses anumber of components (filter, amplifier, etc.) not important to ourpresent discussion. It will suice for present purposes to observe thatits function is to supply air at a predetermined constant pressure tothe cartridge 16 and to indicate on a gage shown generally at 3) thepressure at the inlet kend ,of the cartridge 16 as a function of theclearance area of the nozzle openings 3S (Figs. 2 and 4) which have beenexposed or voided to the atmosphere. The pressure Vsupplied to thepneumatic circuit is adjusted by means of pressure regulator 28.

In'the process of checking the magnification, the air cartridge 16 isbrought successively over the gage blocks so'tlia't the plunger 62 (Fig.2) is in contact with the uppermost block. The cartridge is carefullyadjusted in the clamping means 22 so as to displace the plungeroutwardly or inwardly as the case may be, until the meter needle 34gives the correct indication, i. e., maximum, minimum and zero. As willbe made clear presently the correct calibration requires the carefuladjustment of three factors. (The additional set of hands 32 arepositioned in a plane above the plane of the needle hand 34, and theyVare manually adjustable so as to provide a means for quick visualindication of the permissible maximum and minimum dimensional excursionswhich may `be tolerated.)

When the operator is certain that the correct magnification has beenobtained, he is then ready to begin gaging the work pieces. The plunger62 (Fig. 2) is now placed in contact with the top of work piece 10. Theamount by which the plunger is displaced inwardly or outwardly will berepresented by a needle reading in the positive (oversize) or thenegative (undersize) direction respectively. If the dimensionalindications of the work pieces Vso gaged fall within theangulardisplacement defined by the hands 32 they are within dimensionaltolerance; conversely, if they fall without this permissible area thepieces must be discarded or reworked as the case may be.

The operation of checking the pressure vs. clearance curve or checkingthe magnification as it is known in the art, is a rather painstakingprocess because the actual correct setting is a function of threevariables: pressure in the cartridge intake, the amount of restriction.permitted, and the initial clearance. The discussion tofollow'willreveal that an almost infinite number of combinations are possible. Inorder to make these facts more lucid, reference will now be had to Figs.2, 3A, 3B and 3C.

The principles of operation of the air gage are quite simple. Referringnow particularly to Fig. 2, the air fromy the supply passes through thepressure regulator 28 (Figs. l, 2) where it is adjusted approximately tothe pressure recommended by the manufacturer. This pressure is indicatedby gage 37, and in the actual physical embodiment illustrated in Fig. l,the gage is positioned on the rear portion (not shown) of the comparator26 (Fig. 1). After leaving the regulator 28, the air is fed to arestriction 36 which is also positioned conveniently in the practicalembodiment on the far or rear side of the comparator 26. The restriction36 is connected by any suitable conduit or hose 18 to the air cartridge16. The indicating gage 30 is arranged so as to read the pressure in thepassageway between the restriction 36 and the nozzles 38.

Since the opening in the restriction 36 is rather small, there is apressure drop across it when air is flowing. This pressure drop isdirectly proportional to the amount of air owing through the system. Themass ow of air depends upon the nozzle clearance area uncovered by theplunger 62. The plunger 62 is urged toward contact with the work piecebeing gaged, so that the area of the nozzles open to the atmosphere is afunction of plunger displacement, and hence, of the dimension beinggaged.

Assume that the manufacturer has specified a pressure of 42 lbs. Withthe plunger held inward with the fingers, the nozzles 38 will becompletely closed and the pressure on each side of the restriction 36will read 42 lbs. (This is point 44 on the pressure vs. clearance curveshown in Fig. 3A.) With the nozzle completely open to the atmosphere,the air pressure will approach the so-called open nozzle pressure (Fig.3A: 42). In this case the pressure across the restriction is about 38 p.s. i. so that the back pressure (i. e., the reading of gage 30) is42-38=4 p. s. i.

As will be seen from Fig. 3A, as the nozzle clearance (area opened tothe atmosphere) increases, the back pressure falls oif, and nallyasymptotically approaches the open nozzle pressure 42 of about 4 p. s.i. For the most part this relationship between pressure and clearance issubstantially non-linear, so that only a small portion of the curve (Ato C) is sufficiently linear to be useful for the kind of measurementsso necessary for accurate gaging. However, more than being merelylinear, the manufacturer has carefully selected the operr ating curve sothat as the nozzle clearance increases in equal increments, the pressurefalls off in equal increments. Thus in Fig. 3A:

ADl: AD2 AP1= APa In the `art, the mid-point B (Fig. 3A) is called theinitial clearance, and the end points A and C are related toV thecalibration on the dial of meter 30.

The problem for the customer who wishes to use this gage is to find thisexact curve, and in prior art practice this has been strictly ahit-and-miss affair as will presently be made clear.

The prior art operator in setting up his equipment adjusts the pressureregulator 28, so as to approximately approach the pressure recommendedby the manufacturer. Then the plunger 62 is placed in contiguousrelation with the three settingsof gage blocks or similar standardspreviously referred to and the cartridge is physically adjusted untilthe meter 30 gives the correct deection. The gage should have a maximumusable range from A to C. However, the process of finding this exactposition on the first, or atlbestna few tries, is strictly a fortuitousmatter. Note that three variables are involved, the pressure 30, theamount of opening in the restriction 36 and the initial clearance. Forexample if the operator notices that his maximum reading coincides withpoint A, but that his minimum falls short of C, he does not know whetherto adjust yhis lpressure regulator 28, or the restriction 36, or tolocatea new initial clearance point since it is possible that hisinitial clearance point may be far down enough on the straight lineportion (A-C) so that his minimum deflection means that he is operatingon the lower, and hence'non-linear portion of the pressure vs. clearancecurve.

These difficulties may be more clearly explained by reference to Figs.3B and 3C. First, referring to the family of curves shown in Fig. 3B, ifthe pressure 37 is held constant, and the restriction 36 made smaller,the backk pressure 30 falls off more rapidly, and there is a greatermagnification. Assume that the operator has selected 4B1H as hisuinitialclearance, and that his pressure regulator 28. is held'at a fixed value.As the restriction 36 is closed more and more, the back pressure falls omore rapidly and we obtain the family of curves shown. If the operatormakes no `adjustment: in his initial clearance, it wouldfall along theintersection of the line 46 with the selected curve, and he would beoperating more and more in the non-linear portion. Hence, afteradjusting thewrestriction 36, the operator must locate a new initialclearance point which will be along the line 48. When he has-locatedsuch a point he is not finished, because he must check the magnificationto see that: (a) equall'increments of clearance produce equal incrementsof pressure, and (b) that he is making full use of the dial, i. e., themovement is from A to C (120 of needle displacement). The result (a)will not obtain unless the slope of the lstraight line AC (Fig. 3A) iscorrect, and even if (a) is obtained the operator will not be able touse the manufacturers calibrated scale unless he also satisfies (b).

` Referring now to Fig. 3C, assume that the restriction 36 is held at aconstant setting, and that an initial clearance B2 is selected. If theoperator selects pressure 37 to be varied, the family of curves obtainedwill be that depicted in Fig. 3C. If the initial clearance is unchanged,the zero point will be along the line 50, while the true zero should bealong the line 52. Again the operator must check the magnification forequal increments and the total needle displacement. i

l The air cartridge in accordance with the present invention i-s sho-wnin Fig. 4. The cartridge 16 comprises five main parts: a barrel portion54, a plunger 56, a step ring 58, a thimble 60, and a contact member 62.i

Referring now to Figs. 4, and 6, the barrel 54 is threaded at 64 toreceive fitting 20 (Fig. 1), and is centrally bored at 68 to receive thepiston means or plunger 56. The barrel is further provided with twolongitudinal slots '70 (Fig. 6) cut on diametrically opposite sides ofthe barrel, so as to communicate lthe bore 68 with nozzles 38.

A sleeve 66 (Fig. 4) having a plurality of nozzles 38 is pressed overthe barrel 54, the nozzles communicating with slots 70 so as to providedirect passage from the bore 68 to the atmosphere.

The plunger 56 (Fig. 4) includes two bearing portions 56a and S6b, whichare in sliding contact with bore 68, and a stem portion 56a` of reduceddiameter. As will be readily yseen at this point, as the plunger isreciprocated within the bore 68, the slots or ports 70 are more or lessvented to the atmosphere so that more or less air is a1- lowed to escapeto atmosphere. Bearing portion 56a of the plunger 56 is internallythreaded to receive the threaded portion 62a of the contact member 62.With the contact member 62 screwed into plunger 56 by means of threads62a there is defined a shoulder portion 62b as indicated in the drawing.

The barrel 54 (Fig. 6) is reamed to two diiferent diameters at thethreaded end 64 to provide the reamed holes 72 and '74, the hole 72 andthe bore 68 defining shoulder 72a. The hole 72 is slotted at 75 (Figs.4, 5, 6) to receive the tail end of a pin 78.

A washer 76 having four notches 76a (Fig. 5), and an outside diameterless than that of bore 72, is mounted on the stem portion 56e of theplunger, and is arrested against displacement in one direction by meansof a pin 78 passing through the stem portion 56C. The function of thenotches 76a is to permit the free passage of air into the chamberprovided by reamed hole 72 in cooperation with the piston member 56. Asmay be seen from a study of Figs. 4 and 5, the tail or longer end of pin78 is fitted into the slot 75 'so as to prevent rotational displacementwhile permitting limited displacement axially of the bore 68. A spring80 (Fig. 4) is mounted between the shoulder 72a and the washer 76, sothat the plunger is resiliently urged to the left or intake end of thebarrel.

The barrel 54 at the opposite end includes a reduced diameter portion82, upon which are mounted the step ring 58 and the thimble 60. Thereduced diameter portion 82 is slotted at 84 (Figs. 4, 6) to receive arubber O-ring or any similar packing. The function of the rubber ring orpacking is toprovide `some friction so that the thimble 60 will not beaccidentally rotated or displaced by small forces over which the thimbleis passed.

As may be seen from Figs. 7 and 8, the step ring 58 is provided withsteps or projections 58a, 58b, 58C, and in this particular embodiment,the step from 58a to 58b is .001 in. The thimble 60 has a projection 60awhich by rotation may be brought into successive 58band 58e.

In operation of the device, the air cartridge is connected to the aircomparator 26 as shownin Fig. 1. For this particular illustrativeembodiment, the pressure regulator 28 is set for 42 lbs. Thegage 30(Fig. 2) provided with this comparator is calibrated to correspond to.002" movement of the plunger 62 when the needle hand 34 moves throughthe complete of arc (Fig. 3A: ABC). The marks 40a and 40b are half-waybetween AB and BC and therefore they represent -l-.0005 and .0005respectively.

Next the thimble 60 is rotated so as to contact the high step 58a asshown in Fig. 8. The contact member 62 is pressed back by hand againstthe face 60b of the thimble 60. The air restriction 36 is then openedslowly until the needle 34 points to the -.0005 division (Fig. 3A: 40b).Next, the thimble 60 is rotated to the lowerstep 58b (Fig. 7) and thecontact member 62 is again depressed by hand as far as it will travel.The needle 34 will now swing to the -l-.OOOS divisin (Fig. 3A: 40a). Thereason why this will always be so arises from the fact that the exactposition of the steps has 'been determined empirically for each piece bythemanufacturer (by accurately preparing face 6011). The operator is nowon the linear portion of the pressure vs. clearance curve, and themagnilication is correct. In other words, the linear portion YAC (Fig.3A) has been definitely located so that:

The only task remaining for the operatoris to locate the initialclearance point B. This can readily be accomplished because any initialclearance point selected will be along line AC, the only problem beingfor the operator to correctly locate the mid-point by physicallyadjusting the cartridge unit 16 in the clamping means 22.

While a specific embodiment has been shown and described, it will, ofcourse, be understood that various other modifications may yet bedevised by those skilled in the art which will embody the principles ofthe invention and found in the true spirit and scope thereof.

We claim as our invention:

l. An air cartridge of the type described for use with a pneumaticgaging arrangement including a variable source of air under pressure andan adjustable restriction means connected in series relation comprisinga barrel member having a longitudinal bore therein and passagesproviding communication between said bore and the atmosphere, saidbarrel member having an intake end and a remote end, said intake endbeing serially connected to said source of air under pressure and tosaid adjustable restriction means, a plunger mounted for axialdisplacement within said bore and adapted to uncover said passages tothe atmosphere as a function of said axial displacement, and Calibratingmeans mounted on vsaid barrel member for determining the settings ofsaid variable source of air under pressure and said adjustablerestriction means as a function of specific displacements of saidpiston, whereby the air cartridge may be quickly calicontact with58a,

` brated to provide a linear relationship between the pressure in theintake end of said barrel member and said axial displacement over apreselected pneumatic range.

2. An air cartridge according to claim 1 including spring means forresiliently urging the plunger toward the intake end of said barrelmember, and a contact member secured to the plunger and having an endfor contiguously engaging a work piece being gaged, the contact memberbeing secured to the end of the plunger in proximity to said remote end.

3. An air cartridge according to claim 1 including a contact membersecured to the plunger, said contact member having an end forcontiguously engaging a work piece being gaged, said contact memberincluding a shoulder portion adapted toY arrest plunger displacementwhen pressed into engagement with said calibrating means.

4'.` Anair `cartridge Vof the type described for use with a pneumaticcompaiator gage, comprising a barrel member: having a longitudinal boretherein, and a plurality of passages 'providing communication betweensaid bore and the atmosphere, said barrel member having an intake atoneend and a remote end, the intake of said barrel member being,serially connected to a source of air pressure and to a gaging meter onsaid comparator, -a plunger mounted-for axial displacement within saidbore, and adapted to variably permit egress of air through said passagesto the atmosphere, the degree of egress permitted beinga function ofsaid axialr displacement, a ring member having two Calibratingperipheral steps of :predeterminedidimensions, said :ring member beingmounted coaxiallynori the said remote end of the barrel member, athimblehaving-ra,peripheral projection, `said thimble being rotatablymounted coaxially on said remote end of the barrel member, theprojection being in juxtaposition to said peripheral steps and adaptedto engage each step successively to precisely dene the magnitude ofplunger displacement during calibration, whereby the pneumatic-comparator gage may be quickly adjusted in two steps to provide apressure in the intake of the barrel member i' which is a linearfunction of the axial displacement of the plunger over the'range of saidgaging meter.

5. An air lcartridge of the type described for use with a pneumaticcomparator gage, comprising a barrel member having a longitudinal boretherein and a plurality of slots positioned around a circumference ofsaid bore, a sleeve member having a plurality of nozzles, said sleevemember vbeing mounted on the barrel member and arranged so that saidslots and nozzles provide a plurality of ,passages t'o the atmosphere,said barrel member having anintakeat one 'end and a remoteV end, theintake of said barrel member being adapted for serially connecting to asource ofrair pressure and to a gaging meter on said comparator, aplunger member mounted for axial displacement within said bore andadapted to variably uncover said slots to the atmosphere as a functionof said axial displacement, said plunger member comprising spring meansresiliently urging said plunger member toward the intake of said barrelmember and a contact piece secured to the plunger member and having anend for contiguously engaging a work piece, a ring member having twocalibrating peripheral steps of predetermined dimensions, said ringmember being mounted coaxially on the remote end of said barrel member,a thimble having a peripheral projection, said thimble being rotatablymounted coaxially on the remote end of the barrel member, the projectionbeing in juxtaposition to said steps and adapted to engage each lstepsuccessively to precisely define the magnitude of plunger memberdisplacement during calibration, whereby the pneumatic comparator gagemay be quickly adjusted in two steps to provide a pressure within theintake of said barrel member which is a linear function of the axialdisplacement of the plunger member over a selected range,

References Cited in the le of this patent UNITED STATES PATENTS2.504,212 Mennesson Apr. 18, 1950

